FATTY SUBSTANCES (GENERAL METHODS) 371
A. DETERMINATION OF THE WATER. A flat-bottomed dish containing
about 25 grams of coarse siliceous sand, previously ignited, and a glass rod,
is dried at 100-105° and weighed. About 10 grams of the sample are then
weighed exactly in the dish and mixed weU with the sand. The dish is
then heated in an oven at 100-105° and weighed at intervals of an hour
until two successive weighings are not appreciably different. The loss in
weight gives the water; the residue is utilised for determination C.
B. EXTRANEOUS (NON-FATTY) IMPURITIES. An exact weight (10-20
grams)joi the substance is dissolved in a beaker in petroleum ether (b.pt.
below 70°) by heating gently on a water-bath. The solution is filtered
through a filter dried at 100-105° and tared, the insoluble matter being
washed on the filter with petroleum ether until a few drops of the nitrate
leave no residue on evaporation. The filter and its contents are then re-
dried at 100-105°, and reweighed, the increase giving the non-fatty matter.
This may also be deduced by subtracting water + total fat from 100.
C. TOTAL FATTY SUBSTANCE. The residue from A is placed in a filter-
paper cartridge or capsule and extracted with ether or petroleum ether
(b.pt. below 70°) in an extraction apparatus. The ethereal solution is
collected in a tared dish, evaporated on the water-bath and the residue
dried at 100° and weighed.
To obtain the total fatty matter in the case of partially saponified fats
(refinery residues and similar products) it is necessary to treat with ether,
to shake with dilute sulphuric acid to decompose the soaps, to wash the
ethereal liquid with water, to filter and evaporate it, and to dry the residue
at 100° and weigh it. In this case the process indicated for turkey red
oil (2) may also be followed (see next chapter). .-H
If the respective quantities of free and saponified fats are required, the
substance is first extracted alone with petroleum ether, the extraction
being then repeated in presence of an acid.
2. Objective Characters
These characters are of importance in the analysis o.f fats, since, from
the physical condition, colour and odour, at least an approximate idea of
the nature of the substance may be obtained. Thus, thejsmell is sufficient
to indicate whether a product is olive oil, tallow, palm oil, wool fat, etc.
3. Specific Gravity
This may be determined by means of a Westphal balance or picnometer
at 15° with a liquid fat or at a higher temperature with a solid fat. In
the latter case, determinations at 100° are especially convenient; the fat
is placed in a wide test-tube immersed in a paraffin bath heated at 100°,
a densimeter or the float of a Westphal balance being immersed in the fat
when the latter reaches a temperature of 98° or 100°.
The Italian official methods prescribe the determination of the specific
gravities of oils with the picnometer or with the hydrostatic balance to the fourth
decimal figure at 15°. When the measurements are made at higher or lower
temperatures, 0-00064 is added or subtracted per degree above or below 15°.
The specific gravity may give an indication of the nature of an oil or fath are